A brief history of Land Surveying
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The earliest surveying instrument: The
Plumb Bob
 The
observation that a heavy object hanging from a string
causes the string to hang perpendicular to the earth
is easily made.
By 2600 BC, we know the Egyptians
had taken this concept and created the earliest
surveying instruments: the plumb board, the A-Level,
T-Level and plumb square. This was the first use
of the plumb bob, against a wood frame that paralleled
the surface being measured. The worker could then
make a more precise visual judgment as to the trueness
of plumb or horizontal level. These earliest bobs
were stone and their shape, although often egg-like,
really didn't matter. These simplest of tools remained
virtually unchanged for the next 4400+ years.
The invention of the spirit level,
and the beginnings of the Industrial Revolution
that allowed the level to be manufactured, both
accurately and cheaply, began the demise of the
ancient plumb tools. For establishing plumb and
true horizontal the level is simply a better tool.
It is quicker and easier to use and just as accurate.
But there is one thing the level can't do easily,
and that is to transfer an exact point from one
height to another. The plumb bob is still an indispensable
tool in modern construction.
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Archaeological
records show the use of length standards earlier
than 2000 BC. An Egyptian wall painting (c.
1400 BC) depicts workmen measuring with a
knotted line similar to a modern surveyor’s
chain. |
Early surveying units:
- The link (7.92 inches).
- The fathom (5.5 feet).
- The rod/ perch (3 fathoms or 16.5 feet).
- The chain (66 feet).
- The furlong or furrowlong (660 feet)
- The mile (5280 feet or 1760 yards).
- The league (3.125 miles or 16500 feet...also
198000 inches, 25000 links, 3000 fathoms, 1000
rods/ perches, 250 chains, 25 furlongs or furrowlongs).
Early standards of length were based on body measurements.
The cubit was the distance from elbow to finger
tip, while the foot, palm and finger units are self-explanatory.
Among the earliest length measures was the foot,
which understandably varied from district to district,
and occurred in two common sizes. The first is the
foot of 246 to 252 mm based on a man’s unshod
foot. The second foot measures 330 to 335 mm and
is based on hand measurements.
Other units derive from the Roman, Saxons, Angles
and Jutes who each invaded England at some time.
The rod, furlong and acre are all of Saxon origin.
The mile is a compromise between the French derived
Old British mile and the Roman milliarius.
The origin of the ROD as
a unit of measurement
A traditional unit of distance equal
to 5.5 yards (16 feet 6 inches or exactly
5.0292 meters). The rod and the furlong
were the basic distance units used by
the Anglo-Saxon residents of England
before the Norman conquest of 1066.
The Saxons generally called this unit
the gyrd, a word which comes down to
us as the name of a different unit,
the yard. "Rod" is another
Saxon word which meant just what it
means today: a straight stick. The Normans
preferred to call the gyrd a pole or
a perch (a word of French origin, meaning
a pole; see perche). The length of the
rod was well established at least as
early as the eighth century. It may
have originated as the length of an
ox-goad, a pole used to control a team
of 8 oxen (4 yokes). Scholars are not
sure how the rod was related to shorter
units. It may have been considered equal
to 20 "natural" feet (actual
foot lengths; see foot), or it may have
been measured "by hand" as
30 shaftments. In any case, when the
modern foot became established in the
twelfth century, the royal government
did not want to change the length of
the rod, since that length was the basis
of land measurement, land records, and
taxes. Therefore the rod was redefined
to equal 16.5 of the new feet. This
length was called the "king's perch"
at least as early as the time of King
Richard the Lionheart (1198). Although
rods and perches of other lengths were
used locally in Britain, the king's
perch eventually prevailed. The relationship
between the rod and the other English
distance units was confirmed again by
the Parliamentary statute of 1592, which
defined the statute mile to be either
320 rods or 1760 yards, thus forcing
the rod to equal exactly 5.5 yards or
16.5 feet.
© Russ Rowlett and the University
of North Carolina at Chapel Hill
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The Magnetic Compass
 The
magnetic compass is one of the most important instruments
in the history of surveying. The compass was probably
invented by the Chinese during the Qin dynasty (221-206
B.C.). Chinese fortune tellers used lodestones (a
mineral composed of an iron oxide which aligns itself
in a north-south direction) to construct their fortune
telling boards.
Eventually someone noticed that
the lodestones were better at pointing out real
directions, leading to the first compasses. They
designed the compass on a square slab which had
markings for the cardinal points and the constellations.
The pointing needle was a lodestone spoon-shaped
device, with a handle that would always point south.
Magnetized needles used as direction pointers instead
of the spoon-shaped lodestones appeared in the 8th
century AD, again in China, and between 850 and
1050 they seem to have become common as navigational
devices on ships. The first person recorded to have
used the compass as a navigational aid was Zheng
He (1371-1435), from the Yunnan province in China,
who made seven ocean voyages between 1405 and 1433.
Inventors
with Mary Bellis
Shown: Early B. Rittenhouse Surveyor's Compass
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